1. Field of the Invention
The invention relates generally to optical communication networks, e.g., time-domain wavelength interleaved networks.
2. Discussion of the Related Art
FIG. 1 schematically shows an exemplary conventional Time-domain Wavelength Interleaved Network (TWIN) 10. The TWIN 10 includes a passive optical network (PON) 12 that physically interconnects a number of edge nodes 14. The PON 12 has a plurality of internal nodes 16. Each internal node 16 has an optical cross-connect (OXC) that is configured to passively route optical communications between a plurality of optical transmission fibers 18 based solely on wavelength. Each edge node 14 includes a wavelength-tunable optical transceiver (not shown). Thus, the edge nodes 14 serve as sources and destinations for optical communications carried between end users by the TWIN.
In the TWIN 10, each wavelength-channel is uniquely assigned to one of the edge nodes 14 for receiving optical communications. Then, a source edge node 14 transmits an optical communication to a desired edge node 14 by simply transmitting the optical communication to the PON 12 on the wavelength-channel that has been assigned to the desired edge node 14. The PON 12 routes the optical communication to a desired destination edge node 14 based solely on the wavelength of the optical communication. To transmit to a second destination edge node 14, the source edge node 14 simply resets the transmission wavelength of its optical transceiver to the wavelength-channel that has been assigned to the second destination edge node 14.
Thus, the PON 12 handles routing of optical communications automatically. That is, optical communications do not need label or address headers to enable routing. The wavelength alone ensures that one of the optical communications will be routed to the desired destination edge node 14.
For that reason, the PON 12 does not have hardware support for buffering optical communications at its internal nodes 16. The internal nodes 16 automatically and immediately route received optical communications towards their destination nodes. Furthermore, the OXCs of the PON 12 can simultaneously route multiple optical communications so that collisions between different optical communications do not cause information loss at the internal nodes 16 of the PON 12. In particular, a collision between two optical communications will cause a collision at one of the destination edge nodes 14. Thus, scheduling optical communications to not have overlapping arrival times at the destination edge nodes 14 typically avoids such collisions.
In particular, the PON 12 implements a topology of directed trees in which each edge node 14 is a root of a corresponding one of the trees. Each directed tree routes received optical communications via associated internal nodes 16 to the tree's root, i.e., the destination edge node 14. In such a topology, contention between optical communications occurs at the destination edge nodes 14. To reduce such destination contention, source edge nodes 14 schedule transmissions of optical communications as bursts and interleave bursts to different destination edge nodes.